Currently, overshots are used to externally catch stuck fish during oil field operations. Existing overshots are designed to catch a range of fish of approximately ⅛″, varying between tools of different sizes. During fishing operations, it is very common that the object the operator is trying to engage has not maintained its original outer diameter (“OD”) due to wear. This unknown wear often prevents the overshot from engaging the fish on the first attempt and, therefore, can result in sometimes 2 or 3 trips downhole with smaller sized grapples to catch the fish. As a result, the cost and time of the fishing operation can be significantly increased.
In addition, problems can arise when the grapple engages larger fish. In such instances, the tension rings of the grapples can experience very large stresses at the ring concentration points which may result in the yielding of the grapple. Prior art tools that directly address the yielding of the ring due to engaging a larger range of fish are not immediately available. However, prior art tools have utilized a completely reduced OD on the grapple ring in order to reduce the stress. This feature of the prior art, however, is disadvantageous because completely reducing the ring limits the ability of the grapple to stay in contact with the control finger or other devices used to transfer torque.
Moreover, as the catch range of prior art overshots is increased, the corresponding required internal bowl dimensions require the wall thickness of the bowl to be decreased in order to allow the grapple to expand fully. Accordingly, this limits the maximum catch range of prior art overshots because the bowl wall can only be decreased so much before possible failure.
Accordingly, there is a need in the art for an overshot adapted to efficiently catch a larger range of fish, while reducing the associated stresses and retaining the integrity of the overshot.
A basic assembly for an external fishing tool includes a top sub, a bowl, a standard guide, a grapple (either a basket grapple or a spiral grapple) and grapple controls as shown in FIG. 1. A grapple control usually includes a key and grooves. In some embodiments, a groove on the outer diameter of the grapple control engages a key on the spiral grapple. During fishing operations, after engaging a fish with a spiral grapple, the spiral grapple moves down the bowl with an acceleration sometimes causing a large contact force between the grapple key and the grapple control. An excessive level of contact force may cause the system to fail. There is also need, therefore, for an overshot tool in which mechanical failure of its components, such as the grapple control, upon high contact force is eliminated or delayed.